This invention relates to the field of metal clad, compressed-gas-insulated high-voltage switchgear and more particularly to resistors for use with such a disconnect switch, that prevent flashover through arc suppression and damping.
When switching a disconnect switch, pre-flashover arcs occur, creating wide band high frequency oscillations. Within enclosed high-voltage switchgear, some of the frequencies of said wide band high frequency oscillations can, under certain circumstances, be naturally electrically resonant as a result of the physical dimensions of the enclosed high-voltage switchgear, thereby producing standing waves through internal reflections within the enclosed high-voltage switchgear. During standing wave conditions, local current peaks can reach such am amplitude that the flashover resistance is reduced to the extent that, at the location of a standing wave current peak, a flashover to the metal enclosure can occur.
One method of preventing the propagation of high frequency oscillations is to use low conductivity, high permeability coatings as shown in U.S. Pat. No. 3,829,707 dated Aug. 13, 1974 and in F.R.G. Offenlegungschrift DE No. 3,216,275 dated Sept. 29, 1983. The low conductivity and high permeability of the coating present a high impedance to dampen high frequency oscillations.
The problem with using metallic coatings as a high frequency oscillation suppressor is two-fold. First, since the number and cross-sectional area of the arcs drawn are not controllable, the resistance of the resistive coating presented during operation varies greatly. Second, since arcs and their chemical by-products in an SF6 atmosphere can and do erode metallic surfaces, the effectiveness as a high frequency suppressant of an iron coating will degrade with use.
The problem of using a lumped resistor instead of a distributed resistive coating is the power dissipation requirements of such a lumped resistor during switching.
It is an object of this invention to provide a resistor fo application in pressurized gas-insulated high voltage switchgear. Another object of this invention is to provide a consistent high resistance to high frequency oscillations as encountered in pre-flashover arcs in high-voltage metal-clad switchgear disconnect switches. A further object of this invention is to provide a resistor having high thermal conductivity suitable for use in high-voltage switchgear disconnect switches.